DataFormComboBoxField allow nulls

[Curt]

My combo is configured in the form's AutoGeneratingField event:

e.DataField = new DataFormComboBoxField()
{
    Label = "My combo",
    ItemsSource = ComboTypeList.comboTypes,
    DataMemberBinding = new Binding("FieldName")
    {
        ValidatesOnExceptions = true,
        NotifyOnValidationError = true,
        Mode = BindingMode.TwoWay
    }
}

I would like my combo to show the "Clear Selection" button, but do not know how to access the property.

[Maya]

Hello Curt,

You can create implicit style targeting RadComboBox and define its clear selection button. For example:

<UserControl.Resources>
    <Style TargetType="telerik:RadComboBox">
        <Setter Property="ClearSelectionButtonContent" Value="Clear me" />
        <Setter Property="ClearSelectionButtonVisibility" Value="Visible" />
    </Style>
</UserControl.Resources>

This style will be applied to each of the combo boxes in your application.

Kind regards,
Maya
the Telerik team

[Curt]

Maya

I don't think that solution will work in my situation.
Defining a style for a RadComboBox doesn't apply to a DataFormComboBoxField.
Any other ideas?

Thanks

[Maya]

Hi Curt,

I am sending you a sample project illustrating the suggested approach. Could you take a look at it and let me know if it will work for you ?  

Regards,
Maya
the Telerik team

[Curt]

Maya
Your technique works fine in the sample, and I marked your post as an answer.
I need to modify my project to use your technique.
Thanks

[Oystein]

Sorry for replying to such an old thread.
I solved the problem mentioned by overriding the GetControl() method in the DataFormComboboxField class.

public class DataFormClearableComboBoxField : DataFormComboBoxField
{
    public DataFormClearableComboBoxField() : base() { }

    protected override Control GetControl()
    {
        var cBox = (RadComboBox)base.GetControl();
        cBox.ClearSelectionButtonVisibility = System.Windows.Visibility.Visible;
        cBox.ClearSelectionButtonContent = "Clear selection";
        return cBox;
    }
}

[Peter]

Hi Maya,

your solution is only viable if all ComboBoxes in the RadDataForm should show the ClearSelectionButton or all should hide this button. 

But there are cases when the user wants to show the ClearSelectionButton only for some of the properties beeing displayed. Unfortunately there seems to be no way to show or hide the button in the Autogenerator. There is noting like 

DataFormComboBoxField.ClearSelectionButtonVisibility  or
DataFormComboBoxField.ContentStyle to modify the appearance of the RadComboBoxes

I have taken Oystein's proposal and derived an extended DataFormComboBoxField class to use in the autogenerator. 

Is there no more elegant way?

(See also my question http://www.telerik.com/forums/modify-appearance-of-radcomboboxes-in-raddataform)
 

/// <summary>
/// This class extends Telerik's DataFormComboBoxField, allowing to modify ClearSelectionButton's visibility.
/// This solves the problem, that in the autogenerator the underlying RadComboBox is not accessible and therefore it is not
/// possible to hide or show the ClearSelectionButton from the autogerator.
/// </summary>
public class DataFormComboBoxFieldEx
    :
    DataFormComboBoxField
{
    public DataFormComboBoxFieldEx() : base() { }

    // Set this field to show or hide the ClearSelectionButton
    public System.Windows.Visibility ClearSelectionButtonVisibility = System.Windows.Visibility.Visible;

    protected override Control GetControl()
    {
        RadComboBox cBox = (RadComboBox)base.GetControl();
        cBox.ClearSelectionButtonVisibility = ClearSelectionButtonVisibility;
        return cBox;
    }
}

[Yoan]

Hi Peter,

I have already answered your ticket containing the same question.

Regards,
Yoan
Telerik